Permeability tuners



July 20, 1965 A. W. SIMPSON PERMEABILITY TUNERS Filed April 15, 1962 United States Patent 3,196,374 PERMEABILITY TUNERS 7 Anthony W. Simpson, Wootton, Engiand, assignor to The Plessey Company Limited, Ilford, England, .a British company Filed Apr. 13, 1962, Ser. No. 188,012 Claims priority, application Great Britain, Apr. 14, 1961, 13,472/ 61 12 Claims. (Cl. 336-130) This invention relates to a variable inductor and particularly to tunable circuits and devices employing such a variable inductor.

It is an object of the present invention to provide a permeability tuner which is of relatively simple construction and which avoids the need to apply bias fields to the inductor in order to vary the inductance of an inductor.

Broadly, in accordance with the present invention there is provided a variable inductor comprising a core of a magnetic material having at least one direction of easy magnetisation in which the core is magnetised, a winding around the core and means for varying the angle between the axis of the winding and the selected direction of easy magnetisation in the core whereby the permeability of the core is varied.

For a better understanding of the invention reference will be made to the accompanying drawings in which:

FIGURE 1 schematically illustrates a tuning device incorporating a variable inductor in accordance with the present invention, and

FIGURE 2 shows a perspective structural view of the device of FIGURE 1 with electrical components omitted.

The inductor includes a core 1 mounted on a shaft 2, e.g. by an adhesive. The shaft 2 is rotatably mounted as shown in FIGURE 2. A winding including two coils 3 and 4 is wound around the core which has one or more particular directions of easy magnetisation i.e. uni-axial or multi-axial anisotropy. The coils 3 and 4 are of a wire which has a stiffness such that when wound around the core the coils remain in position Without further support. The core 1 i arranged to be rotatable within the coils 3 and 4 so that the angle between the direction of easy magnetisation of the core and the axis of the coil can be selectively varied. The coil 4 is connected across terminals 5, and the coil 3 is connected to terminals 6 (FIGURE 1). Capacitors 7 and 8 are connected across the ends of the coils 4 and 3 respectively. When the inductor is used as a band pass tuner for radio or television purposes the terminals 6 can be connected one to an aerial and the other to earth. Conveniently the shaft 2 can be provided with a pointer 9 which co-operates with a suitably calibrated scale 10.

Upon rotation of the core within the coil the inductance of the coil will vary. This is due to the fact that the permeability of the core will have a maximum in the easy directions of magnetisation and a minimum in the hard directions'of magnetisation. Thus when the coils form part of a tunable circuit the circuit can thus be selectively tuned.

The actual shape of the core 1 will depend primarily upon the nature of the anisotropy utilised. The materials can either be metallic or oxides in the form of single crystals with a natural anisotropy or materials with magnetic induced anistropy or materials constructed so as to have orientated particle structure.

The actual selection of the material will depend upon the frequency at which the inductance is expected to work and the required form of the variation of inductance with respect'to the angle of rotation of the core within the coils.

For example, a variable inductance for use in high frequency may be constructed from a thin disc ofa crystal orientated ferrite material for example a suitable material of a type known by the trade name Ferrox Planar whose easy direction of magnetisation lies in the base of the plane. If the aforesaid disc is cut from a plane perpendicular to the basal plane, easy direction of magnetisation, of the material the permeability measured in the plane of the disc will show alternate maxima and minima separated by of rotation of the core within the coils.

If desired the two coils 3 and 4 can be replaced by a single coil or more than two coils.

Furthermore the core could be maintained positionally fixed and the winding moved relative to the core.

What we claim is:

1. A variable inductor comprising a core of a magnetic material having at least one direction of easy magnetisation in which the core is magnetised, a winding wound so as to embrace at least a portion of the core and means for varying the angle between the longitudinal axis of the winding axis, about whichthe winding is Wound, and the selected direction or" easy magnetisation in the core whereby the permeability of the core may be varied.

2. A variable inductor as claimed in claim 1, wherein the winding comprises first and second coils.

3. A band pass tuner comprising a variable inductor as claimed in claim 2 and first and second capacitors connected across the first and second coils of said inductor.

4. A variable inductor as claimed in claim 1, wherein the core is in the form of a single crystal having natural anisotropy.

5. A variable inductor as claimed in claim 1, wherein the core is constituted by a magnetic material having induced anisotropy.

6. A variable inductor as claimed in claim 1, wherein the core consists of a material having a particle structure orientated in a common direction.

7. A variable inductor comprising a core of a material having uni-axial anisotropy, the core being magnetised along the direction of uni-axial anisotropy, a winding wound so as to embrace at least a portion of the core and means for producing relative movement between the winding and the core so as to vary the angle between said direction and the longitudinal axis of the winding about which axis the winding is wound.

8. A variable inductor as claimed in claim 7, wherein the winding comprises first and second coils.

9. A variable inductor for use at high frequency comprising a core consisting of a thin disc of a crystal orientated ferrite material having an easy direction of magnetisation in it basal plane, a winding wound so as to embrace at least a portion of the core, and means for selectively varying the angle between the longitudinal axis of the winding, about which axis the winding is wound, and the easy direction of magnetisation.

10. A variable inductor for use at high frequency comprising a core consisting of a thin disc of a crystal orientated ferrite material having an easy direction of magnetisation in it basal plane, the disc being cut from a plane Perpendicular to the basal plane of the material, a winding wound so as to embrace at least a portion of the core, and means for selectively varying the angle be tween the longitudinal axis of the winding, about which axis the winding is wound, and the easy direction of magnetisation, the permeability measured in the plane of the disc exhibting alternate maxima and minima separated by 90 of rotation of the core relative to the longitudinal axis of the winding.

11. A variable inductor as claimed in claim 10, wherein 3 1 the mean for selectively varying the angle between the References Cited by the Examiner longitudinal axis of the winding and the easy direction UNITED STATES PATENTS of magnetlsation of the core comprises a shaft, the shaft being rotatably mounted relative to the winding and the 2,639,324 5/53 HWVCY X .shaft carrying the disc which is fixed relative to the shaft. 5 2,854,607 9/58 Nlkla et a1 336 110 X 12. A variable inductor as claimed in claim 11, includ- 3012177 12/61 Mortlmer X ing a suitably calibrated scale which is fixed relative to the winding and a pointer which is fixed relative to the JOHN BURNS Pnmary Examiner shaft and which co-operates with the scale. 7 E. JAMES SAX, Examiner. 

1. A VARIABLE INDUCTOR COMPRISING A CORE OF A MAGNETIC MATERIAL HAVING AT LEAST ONE DIRECTION OF EASY MAGNETISATION IN WHICH THE CORE IS MAGNETISED, A WINDING WOUND SO AS TO EMBRACE AT LEAST A PORTION OF THE CORE AND MEANS FOR VARYING THE ANGLE BETWEEN THE LONGITUDINAL AXIS AND THE WINDING AXIS, ABOUT WHICH THE WINDING IS WOUND, AND THE SELECTED DIRECTION OF EASY MAGNETISATION IN THE CORE WHEREBY THE PREMEABILITY OF THE CORE MAY BE VARIED. 